Adaptive Methods in Underwater Acoustics
Adaptive Methods in Underwater Acoustics

Author: H.G. Urban

Publisher: Springer Science & Business Media

Published: 2012-12-06

Total Pages: 763

ISBN-13: 9400953615

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The NATO Advanced Study Institute on Adaptive Methods in Underwater Acoustics was held on 30 July - 10 August 1984 in LLineburg, Germany. The Institute was primarily concerned with signal processing for underwater appl ica tions. The majority of the presentations, when taken together, yield a definite picture of the present status of understanding of adaptive and high resolution processing, setting out the progress achieved over the past four years together with the major problem areas remaining. Major effort was made to obtain a commensurate contribution of tutorial and advanced research papers. It is my hope that the material in this volume may be equally well suited for students getting an introduction to some of the basic problems in underwater signal processing and for the professionals who may obtain an up-to-date overview of the present state of the art. This might be especially useful in view of the controversy and lack of adequate interrelationships which have marked this rapidly expanding field in the past. Practical reinforcement of this picture is provided by the material concerning digital and optical processing technology, giving some guidance to achievable adaptive and high resolution techniques with current processing devices. The formal programme was extended and detailed by a series of six evening work shops on specific topics, during which informal discussions took place among the participants. Summaries of these workshops are also included in these Proceedings.

Spatiotemporal Processing and Time-reversal for Underwater Acoustic Communications
Spatiotemporal Processing and Time-reversal for Underwater Acoustic Communications

Author: Daniel Y. Wang

Publisher:

Published: 2005

Total Pages: 67

ISBN-13:

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High-rate underwater acoustic communication can be achieved using transmitter/receiver arrays. Underwater acoustic channels can be characterized as rapidly time-varying systems that suffer severe Inter Symbol Interferences (ISI) caused by multi-path propagation. Multi-channel combining and equalization, as well as time-reversal techniques have been used over these channels to reduce the effect of ISI. As an alternative, a spatiotemporal focusing technique had been proposed. This technique is similar to time-reversal but it explicitly takes into account elimination of ISI. To do so, the system relies on the knowledge of channel responses. In practice, however, only channel estimates are available. To assess the system performance for imperfectly estimated time-varying channels, a simulation analysis was conducted. Underwater acoustic channels were modeled using geometrical representations of a 3-path propagation model. Multi-path fading was incorporated using auto regressive models. Simulations were conducted with various estimator delay scenarios for both the spatiotemporal focusing and simple time-reversal. Results demonstrate performance dependence on the non-dimensional product of estimation delay and Doppler spread. In particular, it has been shown that when this product is low, the performance of spatiotemporal focusing remains superior to simple time- reversal.

Underwater Acoustic Data Processing
Underwater Acoustic Data Processing

Author: Y. T. Chan

Publisher: Springer Science & Business Media

Published: 2012-12-06

Total Pages: 642

ISBN-13: 9400922892

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This book contains the papers that were accepted for presentation at the 1988 NATO Advanced Study Institute on Underwater Acoustic Data Processing, held at the Royal Military College of Canada from 18 to 29 July, 1988. Approximately 110 participants from various NATO countries were in attendance during this two week period. Their research interests range from underwater acoustics to signal processing and computer science; some are renowned scientists and some are recent Ph.D. graduates. The purpose of the ASI was to provide an authoritative summing up of the various research activities related to sonar technology. The exposition on each subject began with one or two tutorials prepared by invited lecturers, followed by research papers which provided indications of the state of development in that specific area. I have broadly classified the papers into three sections under the titles of I. Propagation and Noise, II. Signal Processing and III. Post Processing. The reader will find in Section I papers on low frequency acoustic sources and effects of the medium on underwater acoustic propagation. Problems such as coherence loss due to boundary interaction, wavefront distortion and multipath transmission were addressed. Besides the medium, corrupting noise sources also have a strong influence on the performance of a sonar system and several researchers described methods of modeling these sources.

Digital Underwater Acoustic Communications
Digital Underwater Acoustic Communications

Author: Lufen Xu

Publisher: Academic Press

Published: 2016-09-16

Total Pages: 292

ISBN-13: 0128030291

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Digital Underwater Acoustic Communications focuses on describing the differences between underwater acoustic communication channels and radio channels, discusses loss of transmitted sound in underwater acoustic channels, describes digital underwater acoustic communication signal processing, and provides a comprehensive reference to digital underwater acoustic communication equipment. This book is designed to serve as a reference for postgraduate students and practicing engineers involved in the design and analysis of underwater acoustic communications systems as well as for engineers involved in underwater acoustic engineering. Introduces the basics of underwater acoustics, along with the advanced functionalities needed to achieve reliable communications in underwater environment Identifies challenges in underwater acoustic channels relative to radio channels, underwater acoustic propagation, and solutions Shows how multi-path structures can be thought of as time diversity signals Presents a new, robust signal processing system, and an advanced FH-SS system for multimedia underwater acoustic communications with moderate communication ranges (above 20km) and rates (above 600bps) Describes the APNFM system for underwater acoustic communication equipment (including both civil and military applications), to be employed in active sonar to improve its performance

Combined Spatial Diversity and Time Equalization for Broadband Multiple Channel Underwater Acoustic Communications
Combined Spatial Diversity and Time Equalization for Broadband Multiple Channel Underwater Acoustic Communications

Author: Violeta Skoro Kaskarovska

Publisher:

Published: 2015

Total Pages: 136

ISBN-13:

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High data rate acoustic communications become feasible with the use of communication systems that operate at high frequency. The high frequency acoustic transmission in shallow water endures severe distortion as a result of the extensive intersymbol interference and Doppler shift, caused by the time variable multipath nature of the channel. In this research a Single Input Multiple Output (SIMO) acoustic communication system is developed to improve the reliability of the high data rate communications at short range in the shallow water acoustic channel. The proposed SIMO communication system operates at very high frequency and combines spatial diversity and decision feedback equalizer in a multilevel adaptive configuration. The first configuration performs selective combining on the equalized signals from multiple receivers and generates quality feedback parameter for the next level of combining. The second configuration implements a form of turbo equalization to evaluate the individual receivers using the feedback parameters as decision symbols. The improved signals from individual receivers are used in the next iteration of selective combining. Multiple iterations are used to achieve optimal estimate of the received signal. The multilevel adaptive configuration is evaluated on experimental and simulated data using SIMO system with three, four and five receivers. The simulation channel model developed for this research is based on experimental channel and Rician fading channel model. The performance of the channel is evaluated in terms of Bit Error Rate (BER) and Signal-to-Noise-and-Interference Ratio (SNIR). Using experimental data with non-zero BER, multilevel adaptive spatial diversity can achieve BER of 0 % and SNIR gain of 3 dB. The simulation results show that the average BER and SNIR after multilevel combining improve dramatically compared to the single receiver, even in case of extremely high BER of individual received signals. The results demonstrate the ability of the proposed multilevel adaptive combining approach to significantly improve the performance of the shallow water acoustic channel, while preserving the same transmission power and channel bandwidth.

Underwater Acoustic Digital Signal Processing and Communication Systems
Underwater Acoustic Digital Signal Processing and Communication Systems

Author: Robert Istepanian

Publisher: Springer Science & Business Media

Published: 2013-03-09

Total Pages: 283

ISBN-13: 1475736177

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Underwater acoustic digital signal processing and communications is an area of applied research that has witnessed major advances over the past decade. Rapid developments in this area were made possible by the use of powerful digital signal processors (DSPs) whose speed, computational power and portability allowed efficient implementation of complex signal processing algorithms and experimental demonstration of their performance in a variety of underwater environments. The early results served as a motivation for the development of new and improved signal processing methods for underwater applications, which today range from classical of autonomous underwater vehicles and sonar signal processing, to remote control underwater wireless communications. This book presents the diverse areas of underwater acoustic signal processing and communication systems through a collection of contributions from prominent researchers in these areas. Their results, both new and those published over the past few years, have been assembled to provide what we hope is a comprehensive overview of the recent developments in the field. The book is intended for a general audience of researchers, engineers and students working in the areas of underwater acoustic signal processing. It requires the reader to have a basic understanding of the digital signal processing concepts. Each topic is treated from a theoretical perspective, followed by practical implementation details. We hope that the book can serve both as a study text and an academic reference.

Examination of Time-Reversal Acoustics in Shallow Water and Applications to Underwater Communications
Examination of Time-Reversal Acoustics in Shallow Water and Applications to Underwater Communications

Author: António Adolfo Mendes Abrantes

Publisher:

Published: 1999-06-01

Total Pages: 91

ISBN-13: 9781423543008

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Time-varying multipath propagation is considered the most important difficulty in shallow underwater acoustic (UWA) communications. To compensate for the time variability of the channel, the receiver must use an adaptive algorithm for adjusting its parameters. At high symbol rates, intersymbol interference caused by multipath propagation requires large adaptive filters, increasing the computational complexity at the receiver end. This thesis presents a time-reversal acoustic technique (implemented with a phase-conjugated array of PCA) that generates a spatio-temporal focus of acoustic energy at the receiver location which reduces distortions introduced by channel propagation (including multipath), allowing the use of low-complexity receivers. Numerical analysis shows that for different PCA geometries (element spacing and aperture sizes), the PCA focus footprint does not appear to significantly change its dimensions. Furthermore, the aperture size plays a more significant role than the number of array elements in a PC array design. Specific examples of novel UWA communication systems utilizing time-reversal focusing are introduced. Current simulation results suggest the potential for high data transfer rates compared to existing noncoherent UWA communication systems.